1. Field of the Invention
This invention relates to an apparatus for controlling the supply of fuel to an internal combustion engine. More particularly, it relates to an apparatus which can control the supply of fuel appropriately in the idling or low load condition of the engine to control the rotation of the engine to a demanded speed when a control valve provided in a bypass passage for a throttle valve has become in an uncontrollable condition in the open position and is incapable of controlling the amount of air being introduced into the engine. This results in an idling speed which is so high that the vehicle in which the engine is installed cannot be driven properly.
2. Description of the Prior Art
Control valves have been provided in a bypass passage extending between the upstream and downstream areas of a throttle valve in an air intake for an internal combustion engine, for controlling the amount of the air being introduced into the engine to thereby control the engine speed at a constant speed during its idling, i.e., when it is driven with the throttle valve maintained substantially in a closed position.
The degree of opening of the control valve is controlled during the idling of the engine in accordance with the amount of any external load required for an air conditioner, or the like, in order to ensure an appropriate supply of air to the engine and correspondingly appropriate supply of fuel so that the engine may produce an appropriate output.
Further, a fuel cutting system has been provided which reduces the supply of fuel when it is driven in a decelerating condition, in order to improve the fuel consumption.
The system functions to cut fuel, for example, when pressure on the accelerator has been released, resulting in substantially the complete closure of a throttle valve. The fuel cutting system ceases to function when the rotating speed of the engine has been reduced to a predetermined engine speed which is slightly higher than the idling speed.
When the engine speed continues to be maintained around the predetermined engine speed in a particular driving condition, the fuel cutting system repeatedly operates by turning on and off, and the operator repeatedly feels sudden changes of engine torque. Hitherto, in order to avoid the changes, the fuel cutting system has a hysteresis area between the engine speeds which stops and starts fuel cutting.
In order to prevent the hunting of the engine, it has hitherto been usual to raise the rotating speed of the engine at which the fuel cutting system functions and lower the rotating speed at which the system ceases to function. Therefore, the conventional fuel cutting system functions to cut the supply of fuel to reduce the engine speed in an area which is shown by broken lines in FIG. 5. It contains a hysteresis area.
The prior art as hereinabove described has the following problems:
(1) In the event an excessive increase in the amount of air being introduced into the engine during its idling has resulted from, for example, the failure of the control valve or a circuit for driving it, the engine is likely to have an increased rotating speed, as fuel is supplied in an increased quantity corresponding to the amount of the air.
Therefore, the engine is likely to hunt heavily around the hysteresis area of the fuel cut area. If the accelerator is pressed to start the vehicle, the fuel cutting system ceases to function and as a result, it is likely that the rotating speed of the engine will increase suddenly, or that the vehicle may start or be accelerated suddenly if the power of the engine is transmitted to the driving wheels (i.e., when the vehicle is in gear).
(2) There is also known a device for detecting any excessive reduction in the amount of the air being introduced into the engine during idling as a result of, for example, the failure of the control valve or the circuit for driving it, and keeping all the valves fully open to increase the amount of the air to avoid engine stall.
In this case, however, the fuel is supplied in an increased quantity corresponding to the amount of the air and the idling of the engine has an increased rotating speed. As a result, there arises the same problems as those stated in (1) above.